At present, lithium ion batteries are becoming increasingly popular in electric vehicles and grid energy storage. Accordingly, more and more attention has been paid to the safety performance of lithium ion batteries. Generally, safety accidents of lithium ion batteries are caused by thermal runaway.
When thermal runaway occurs to a lithium in battery, heat generated by active materials in a lithium ion battery may reach hundreds of Joule/g, which may lead to intense oxidation-reduction reaction of the active materials and the electrolyte and further generate a large amount of flammable gases. The flammable gases generated may lead to sharp increase of pressure in the lithium ion battery and break the explosion-proof valve to generate high speed gas flow. The flammable gases ejecteded will mix with the surrounding air. At the same time, during the ejection of the flammable gases from the lithium ion battery, a large amount of high temperature solid parciles will be brought out. The solid particles may ignite the mixture of the flammable gases and the surrounding air, which may lead to ignition even explosion of the lithium ion battery.
Chinese patent publication number CN 103474599A discloses a lithium ion battery and a lithium ion battery pack having desirable safety performance. The lithium ion battery is equipped with a mesh member which defines a number of through holes extending therethrough. The mesh member can filter the high temperature solid particles, to seperate the high temperature solid particles from the inflammable gases. However, the mesh member disclosed in CN 103474599A at least has the following disadvantages. When thermal runaway occurs to a lithium ion battery, the mixture of the imflammable gases and the high temperature solid particles in the lithium ion battery will be ejected quickly. The through holes are only defined in the top section of the mesh member in the path of the gas ejection. If the through hole of the mesh member is too large, the high speed gas flow brings the high temperature solid particles out, which may lead to ignition or explosion of the lithium ion battery. In addition, if the through hole is too large, the strength of the mesh member is reduced, and the mesh member is apt to break under the impact of the high speed gas flow carrying the high temperature solid particles. If the through hole is too small, the gases cannot be discharged from the lithium ion battery timely. In addition, when thermal runaway occurs to the lithium ion battery, the melted plastic components, the solid particles in the gas flow or the melt slage may block the through holes, which will lead to sharp increase of pressure in the lithium ion battery and even explosion of the lithium ion battery.
In view of the foregoing, what is needed, therefore, is to provide a lithium ion battery and a lithium ion battery pack having desirable safety performance.